1. Field of the Invention
The present invention relates to a gas sensor for detecting the concentration of a gas component contained in a gas to be measured.
2. Description of the Related Art
A specific example of a gas sensor for detecting the concentration of a gas component is the oxygen sensor disclosed in Patent Document 1. The disclosed oxygen sensor has an oxygen detection element which assumes a hollow tubular shape. The oxygen detection element has a closed front end and an opened rear end, and extends along an axial direction. An electrode layer (hereinafter also referred to as an internal electrode layer) is formed on the inner circumferential surface thereof.
In this type of oxygen sensor, while atmospheric air serving as a reference gas is introduced into the oxygen detection element such that the internal electrode layer is exposed to the reference gas, an external electrode layer formed on the outer circumferential surface of the oxygen detection element is exposed to a gas to be measured. As a result, an electromotive force is induced in accordance with the difference in oxygen concentration between the inner and outer circumferential surfaces. This electromotive force, which serves as a signal indicative of the detected oxygen concentration of the measured gas, is led outside the sensor from the internal and external electrode layers via terminal members, lead wires, etc., whereby the oxygen concentration of the measured gas can be detected.
A terminal member for conveying an electromotive force from the internal electrode layer of the oxygen detection element is formed of a member, such as a metallic plate, which has elasticity and electrical conductivity. This terminal member has press contact portions which come into pressure contact with the internal electrode layer of the oxygen detection element to thereby hold the terminal member itself.
Patent Document 1 shows a terminal member having a press contact portion which is formed such that it has a generally horseshoe-shaped radial cross section as viewed in a radial direction perpendicular to the axis thereof and such that, in a free state, the diameter of a circumcircle of the radial cross section (a circle circumscribing the radial cross section) is larger than that of the inner circumferential surface of the oxygen sensor. When the terminal member is assembled into the oxygen detection element, because of elasticity of the terminal member, two tip end portions and a base-side center portion of the terminal member as viewed in the generally horseshoe-shaped radial cross section serve as press contact portions which come into press contact with the inner circumferential surface of the oxygen detection element. By means of the pressing force of the press contact portions, the terminal member is held within the oxygen detection element and is brought into press contact with the internal electrode layer. Simultaneously, electrical continuity is established between the internal electrode layer of the oxygen detection element and the press contact portions, whereby an electromotive force can be conveyed from the internal electrode layer of the oxygen detection element to the outside via the terminal member.    [Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2001-66281 (FIGS. 1, 3, and 8)